1. Field of the Invention
The present invention relates generally to a method of packing comprising the steps of intermittently conveying a strip-like bag material which comprises a series of interconnected plastic bags, packing goods into a foremost bag portion of the strip-like bag material, thereafter sealing the bag portion and separating the sealed bag portion from a subsequent bag portion of the bag material, and more particularly, it relates to a method of conveying such bag material in a packing machine for carrying out said method of packing.
2. Description of the Prior Art
In general, the strip-like bag material as used in packing machines for carrying out such method of packing is of the structure as illustrated in FIGS. 2 and 3. The striplike bag material A shown in these Figures is made of a collapsed film tube of a thermoplastic synthetic resin such as vinyl or polyethylene which is manufactured by an extruder with an inflation device, and comprises a series of interconnected bags 6. The strip-like bag material A is provided with a plurality of transversely extending rectilinear welded portions 2 which form bottoms of the bags 6 and which are formed by heat-sealing the bag material transversely across the same at regular intervals by a heat-sealer. Also, the bag material A is provided, on one side thereof, with transversely extending rectilinear opening portions 3 which are respectively located at portions adjacent to the respective welded portions 2 at regular intervals and in parallel relationship therewith, whereby flap-like margins 4 of the welded portions 2 are formed transversely across the bag material A between the opening portions 3 and the welded portions 2, respectively. Further, the bag material A is provided, on the other side thereof, with easily severable rectilinear fragile portions 5 which are formed across the breadth of said bag material on the other side thereof at portions opposite to the opening portions 3, respectively. In the illustrated embodiment, each of the rectilinear fragile portions 5 takes the form of a row of discontinuous perforations.
Usually, a packing operation with the use of the strip-like bag material A is performed as described below. First, the strip-like bag material A is wound into the form of a roll as shown in FIG. 1, then the rolled bag material is supported on a roll support 13 of a packing machine P and then the leading end of the rolled bag material A is drawn. Thereafter, the bag material A is pinched between a pair of intermittently operated pinching rollers 8 after being passed over a plurality of guide rollers 7 in such a way that its leading end depends from the pinching rollers 8 into a goods-charging device 9 located beneath the same. Under this condition, the bag material A is conveyed, by actuating the pinching rollers 8, for a distance corresponding to the length l of a single bag 6, then during an inoperative interval of the rollers 8, the foremost bag 6 is inflated by actuating an air blower 10 so that goods 11 can be smoothly packed into the foremost bag 6 and then after the goods have been packed, operation of the blower 10 is stopped and the bag is sealed along its opening portion 3 by means of heat-sealers 12 and finally, the goods-charged bag 6 is separated from the subsequent bag 6 of the bag material A at the fragile portion 5 of the goods-charged bag. Thereafter, such packing operation can be repeated by operating the pinching rollers 8.
To ensure intermittent transfer of the strip-like bag material A for a distance corresponding to the length of a single bag, two methods have hitherto been proposed. One of the methods employs photoelectric elements and the other of the methods a pair of electrodes as means for controlling transfer of the bag material, respectively. The former may only be applied in case where printed patterns, letters, register marks or the like are indicated on the respective bags of the bag material, while the latter is applicable only in case where openings, cut-outs or the like are formed in the respective bags. In addition, the former has such drawbacks that when the bag material is transferred at a high speed, such register marks or the like cannot be accurately scanned by the photoelectric means, which causes the bag material to be transferred for a distance not corresponding to the length of a single bag of the bag material, thus causing incomplete packing. Also the provision of the photoelectric means requires a great expense. On the other hand, the latter method has also such additional drawbacks that the use of electrodes requires considerably high voltage which causes a danger of injuring operators and that the scanning capacity of the electrodes is relatively low.